The objective of the proposed research is to study the processes of potassium transport by the kidney, to determine the relationship of these processes to Na and Cl transport and to study the effect of acid-base disturbances upon them. The isolated perfused bullfrog kidney will be used. Techniques have been established to: 1) Obtain comparative values for the unidirectional fluxes of K between the circulation and tubular fluid using 42K. 2) Measure the rate constants for the effluxes of K from the epithelium into the circulation and tubular fluid. 3) Measure the rates of uptakes of K by tubular cells from the circulation. These techniques will be utilized in experiments in which the rates of Na and Cl transport have been decreased by reducing their concentration in the perfusates and by using transport inhibitors. Such experiments should provide information on the relationship between the secretory flux of K and Na reabsorption, on the effect of changes in Na transport on K uptake by tubular cells from the circulation and the influence of Na on the rate of loss of K from these cells into the tubular fluid. A reduction in the Cl concentration of the perfusates has been shown to inhibit K reabsorption and to stimulate K secretion. These experiments will help determine if these effects are due to inhibition of Cl reabsorption and if the effect on K secretion occurs at the apical or basolateral face of tubular cells. The relative influence of alterations in pH, PCO2 and bicarbonate concentrations in tubular fluid, peritubular fluid and cells on these components of K transport will also be studied.